Mark I G.P.S. CLOCK — The Beginning (2008).

The Mark I G.P.S. CLOCK began in 2008 when the Bristol 70cms Repeater Group asked us to solve a practical problem: their RC210 repeater controller kept drifting out of time. Our solution was straightforward — use GPS to obtain accurate UTC and send a corrected time string to the RC210 once per hour. The Mark I proved the concept immediately.

It was built entirely from whatever we had in the workshop: a second‑hand Trimble GPS receiver, a PIC16C84 on strip‑board, and a generic ABS project box. It was meant to be a one‑off, built for free, just to help the repeater group.

Once the Trimble achieved a 4‑satellite lock, the 16×2 LCD displayed the UTC time and date. No menus, no configuration — deliberately simple.

Despite its improvised construction, the Mark I ran reliably in a live repeater environment. Ok, users weren’t thrilled that the Repeater only used UTC throughout the year and comments passed to us were not always in the spirit of amateur radio shall we say.  Further expansion could not take place as the MK I being a one off could not be taken out of service. On top of this, the IDE we had used for programming was not the most friendliest and the PIC itself was limited and (in our view) had a horrible architecture.